Loaded signaling conductor and method of signaling



June 10, 1930. J. J. GILBERT 1,753,041

LOADED SIGNALING CONDUCTOR AND METHOD OF SIGNALING Filed Ma rch 5, 1924 3 Sheets-Sheet 2 perm Inductance //7 van for Jab/7d GV/ker/ June 10, 1930. .J. J. GILBERT 1,763,041

LOADED SIGNALING CONDUCTOR AND METHQD OF'SIGNALING I File d March 5, 1924 s Sheets-Sheet s A/fy .- currents. A'specific object of the invention Patented 1.....10, 1930 UNITED STATES PATENT OFFICE JOHN J. GILBERT, OF PORT WASHINGTON, NEW YORK, ASSIGNOR TO WESTERN ELEC- TRIO COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK "" SIGNALING CONDUCTOR AND METHOD OF SIGNALING Application filed March 5, 1924. Serial No. 690,981.

I This invention relates to inductively loaded. signaling conductors, and in particular to long submarine cables.

The main object of the invention is to provide a new improved loaded signaling conductor and a new improved method of signaling over a metallic conductor. In accordance with this object, the invention involves the inductive loading of a signaling conductor differently at different points along its length, and, in general, loading it mostheavily in the central portions or portions remote from the terminals and more lightly at or near the terminals. In some cases, the loading is reduced to zero at the terminals; that is, is omitted.

In one aspect of the invention, the grading of'the inductive loading 'is such as to reduce attenuation as much as practicable to produce dnly small distortion in the received current. In another aspect, the grading is for the purpose of decreasing the sending voltage unbalance or, when such unbalancev is .not large, to permit the use of balancing networks whichare less complicated than those heretofore used. From a different point 'of view, the invention comprises the grading'of the loading of a signaling conductor in such manner as to enable theoptimum p'ermeability f the loading materialto be maintained thr ughout the lengthof the loaded conductor. In still another aspect, the invention pertains to grading the loading of a submarine cable for the pur ose of preventing or reducing distortion 0 the signals due to rapid variations of inductance caused by movement of the cable by ocean waves or isthe simultaneous accomplishment of two or more of these purposes to a marked degree by loading a sign entl at different points along its length.

This application is .a continuation,'lin part,

of application Serial No. .57 9,393 filed August 3, 1922.

A 'of the invention which pertainsto reduction aling conductor diiferapplicable to long submarine cables, and the following description is, therefore, confined largely to this type of signaling conductor.

However, certain aspects of the invention are applicable also to other signaling conductors.

Fig. 1 of the accompanying drawin s is a diagram showing the dependence 0 resistance and inductance on current magnitude for a certain continuously loaded line; Fig. 2 is a diagram showing the relative intensity of induced voltage for a certain harmonic as a function of magnitude of the fundamental current in a certain continuously loaded line; Fig. 3 is a diagram showing the fundamental current as a function of distance from the sending end in that line,

Fig. 1 is a diagram of apparatus suitable for the practice of the invention; Fig. 5 is a detail view illustrating degrees ofloading;

Fig. 6 and- 7 are illustrations of modified discussing the designof the system; Fig". 10 1s a curve showing the increase of unbalance efiect with heavier loading and increase of frequency. The specific example here chosen to illustrate the particulars of the present invention, is a modification of that cable and a combination involving the modified cable.

In the specification of Buckley Patent 1,586,874, granted June 1, 1926, it is pointed out that the loading of lon ocean telegraph cables has heretofore been oundof no practical advantage, but that a very great gain in speed is obtained by loading a 2,000 naut cable with a tape of one of a series of mag netic compositions "called permalloy.

A suitable form-of permalloy is obtained by fusing together iron and nickel in the respective proportions of 211/ and (S and forming them into a ta e of suitable dimensions. This'permalloy, ape is applied helically to the conductor with the edges abutting. Thereafter the taped conductor is t given a heat treatment descrlbed in the speci- There first be discussed that aspect loy tape in a condition of very o cation referred to, which leaves the normalhigh permeabillty for low magnetizing rces, many heretofore in use.- 1

times higher'than in the best samples of iron The high permeability of the loading ma terial gives the loaded conductor a high inductance, thus diminishing the attenuation, and facilitates the transmission of signals at much higher wave frequencies than has been possible on the unloaded cable conductors heretofore in use.

In the operation of long ocean cables, it has been usual to operate them duplex. For this purpose artificial lines are provided at both ends, each of which simulates the cable to a practicable degree, and the actual cable and the artificial line are connected up as arms of a Wheatstone bridge. In the Buckley patent, previously referred to,- the continuously loaded line is disclosed as being operated preferably one way, and in the particular example there considered, the one-way operation was shown to be at about times the speed for the unloaded cable with which comparison was proper. The unloaded cable of the prior art has its message capacity increased somewhat less than 100% by duplex operation, so that the message capacity of the continuously loaded cable operated simplex is more than 5 times the message capacity of the unloaded cable operated duplex.

In theoretical discussions of the transmission characteristics of a loaded submarine telegraph cable, it is generally assumed that the cable parameters R, the resistance per naut;

L, the inductance per naut,

G, the capacity per naut, and G, the leakance per naut,

are independent of the amplitude of the current in the cable. The attenuation constant per naut for this ideal cable can then be obtained by means of the well-known formula However, in the case of certain loaded conductors, and particularly in the case of a long signaling conductor continuously loaded with permalloy, the inductance and effective resistance vary to a considerable extent with variations in the current in the conductor in the range of current amplitudes employed for telegraph signaling. This is 'due principally to the fact that the permeability of the permalloy is a non-linear function of magnetizing force, and is also due to the rapid ,increase of hysteresis loss with magnetic flux density. The amount of these variations depends upon the permeability of the loading material and upon the manner in which it is applied to the conductor. For the particular cable of length 2,000 nauts heretofore mentioned, the values of inductance and ef- 00 fective resistance at a given reasonable signaling frequency vary with the current as shown in Fig. 1. As the current increases, both the effective resistance and the inductance increase as shown by the respective curves in Fig. 1. The rate of variation is much less for small values of current than for large values.

This variation of the cable parameters with varying current involves two effects which will now be noticed. First, the attenuation will be greater than the value computed for the ideal cable from the formula heretofore given for a; this is on account of the fact that the resistance increases much faster with cur-. rent amplitude than does the inductance. Second, distortion of the signaling impulse occurs, due to intermodulation between the various frequency components of the transmitted signal, and between the transmitted and the received signaling frequency components where duplex operation is employed.

The magnitude of these phenomena can best be determined by a method of approximation. For purposes of illustration we will consider the case of a short length of loaded conductor for which the inductance and resistance vary with the current in the manner indicated by the formulas,

flows in the conductor the voltage between the terminals of the conductor will be or, using Equation 2, 3 and 4,

' 1 :12,], sin pt+a l (sin pt) +a I (sin pt) 3 +L I p cos pita-26 1 2? sin pt cos pt +319 p (sin pt) cos pt V0+Vo +V 1+V2,

where V0 R I Sin LOPIO COS pt, V0 Tia/210 Sin gbgpl o COS pt,

V =b pl sin nf-$11,1 cos 2pt, v V -%a I sin 3ptib pl cos 3pt.

The resultant voltage can, therefore, be considered as made up of a number of components, which have frequencies equal to, or multiples of, the frequency of the fundamental current, and amplitudes which are functions of the amplitude of the fundamental current. V is the voltage that would exist between the terminals of a conductor having the parameters R and L for all current values when traversed by a current I =1 sin pt. V V and V represent the transmission characteristics the loaded sub-' but with voltage of fundamental, harmonic 1 'forces induced in the conductor which give rise to current-s of the respective frequencies.

The current due to V being of the funda mental frequency, combines with the current I and tends to decrease the amplitude of the latter. The currents due to V and V are of harmonic frequencies and result in distortion of the current wave from its pure sinusoidal shape. The method just described can be applied to the case of a long submarine cable by dividing the cable into a number of short sections and treating each section as a separate conductor,'-integrating'the separate effects in order to obtain the effect for the entire cable.

Thepreceding analysis gives merely a first approximation to the actual conditions in the conductor. The next step would be to replace Equation (4) by the new expression for the current and repeat the process of approximation. For the purposes of the present explanation, however, this first approximation is of sufficient accuracy.

It is evident, therefore, that as regards marine cable here in view is equivalent .to an ideal cable with R and L at all currents equal to the R and L at small current values,

and combination frequencies induced contin uously along the cable, the amplitude of the induced voltage at any point being dependent upon the magnitude of the fundamental current at that point. For'example, when two sinusoidal currents of respective frequencies f and f are being transmitted over-the cable, superposed voltages having the frequencies f 1 7 7 27 1, 7 2, fi' 'fz, f1 -f2, etc.,will

be induced along. the cable and the magnitudes of these induced voltages at any point are functions of the amplitudes of the two fundamental currents at that point. The current due to the induced voltage of fundamental frequency is superposed on the current due to the impressed voltage of that frequency and tends toreduce the amplitude of the latter current, thus simulating the effect previously mentioned, that attenuation in the actual loaded cable is greater than in the ideal loaded cable. The voltages of harmonic and combination frequeiiciesfrepresent the distortion of the signal shape due to the modulation previously described. Themanner in which themagnitude of one of these induced harmonic voltages for example varies with.

the fundamental current is shown in Fig. 2.

For this purpose the second-harmonic (double frequency) is chosen. The amplitude of the second harmonic voltage'is at once seen to be large for the higher values ofcurrent amplitude but falls off rapidly as .the fundamental current is decreased. Thus it will be seen that in a cable practically all theinduccd voltage of harmonic frequencies originates in the neighborhood of the sendi-ngend because it is thereonly that the fundamental current has sufliciently great magnitude to produce this effect. This isevident from Fig. 3, which shows the amplitude of the fundamental current at various distances from the sending end, where the fundamental current is sinu-v soidal and of frequency 60 cycles per second. The fundamental current is reduced in the first few hundred miles of the .cable to a value for which, according to Fig. 2, the amplitude of the induced harmonic voltage is very small.

The induced voltages at any point, of which the second harmonic has been considered by is much less than in duplex operation, be-' cause in the former case the majority of the disturbin voltages, being of high frequency, are consi erably attenuated by transmission over nearly the whole cable from the points where-they are of considerable magnitude. The efiect of the induced volta e of signal frequency, representmg the e ect of increased attenuation, will be strongly felt,

- however, the result of it being to decrease'the In dutransmission efficiency of the cable. plex operatiomlthe induced voltages due to the transmitted signal will interfere seriously with the received signal, since it is practically impossible to simulate in the artificial line,

the conditions that exist in the cable. This is especially true because the effectfat a cable terminal due Ito a transmitted signal persists for a longer 'ime than for the ideal cable with constant parameters, and this effect is likely to be'of an amplitude comparable with that i of the signal from the distant terminal.

Although theforegoing statement has relation primarily to duplex operation, as com-' monly understood, in which there is actual simultaneous, and continuous transmission both ways, it also has a plication in connection with a somewhat di' erent system of twoway transmission; which will now be mentioned. This proposed method of operation involves a few impulses, perhaps only one impulse one-way and then alternately receiving 1 1 may amount to a'cei'tain degree of interference with the first part of the succeeding recei-ved impulses. By the present invention;

80 way of example, give rise to currents of the these efiects near the terminals are minimized and therefore there will be less interference dueto persistence of eifect from a transmitting interval into the succeeding receiving interval.

The magnitude of the currents at the cable terminal due to the induced voltages is a measure of the departure of the cable from the ideal condition of constant parameters, and in order to secure satisfactory operation of the cable, these disturbances must be kept I below a certain limit which depends upon the ability of the receiving apparatus to discriminate between signals and interference.

In the present invention this is accom-' such characteristics can be obtained in a number of ways. For example, by decreasing the permeability of the loading material. not only the inductance, but the rate of change of inductance of the conductor is diminished and the variation of the efiective resistance is much less than in a conductor of higher inductance, since the flux density, and therefore the hysteresis loss, are smaller.

, Another way to decrease the slope of the characteristics is to use a smaller thickness of loading material with normal permeability. The resistance due to hysteresis loss is smaller in this case also, since the volume of material is less. Still another way is to use the normal dimensions and permeability of tape,

' but instead of laying the tape so that the edges ofadjacent turns abut, it is laid so that there is an interval between the adjacent turns, as indicated in Fig.5. This way of decreasing the slope of the characteristics not only reduces the contribution of hysteresis to the eifective conductor resistance, but.

also decreases the variation of inductance by introducing a large air-gap into the magnetic circuit.

' A cable section constructed. by any of the methods above described will have a smaller efiiciency of transmission for that sectionthan a cable in which the normal permalloy loading is employed, since the inductance is diminished along with the slope of the characteristics. It is possible, for instance by the use of a number of parallel layers of loading material, to construct a conductor which has the same transmission efliciency as the normal type of conductor and at the same time possesses characteristics of lesser slope than the normal type. This is due to the fact that for a given efliciency of transmission a lower value of permeability can be used in multiple layer loadin than in single layer loading. This form 0 graduated loading is shown in Fig. 6. The cost of such a conductor, how-' ever, is greater than that of a conductor with only a single layer of loading material. It is obvious that, on the grounds either of cost or transmission eficiency, it is not desirable to construct a cable which employs throughout its length a conductor of any of the special types which have been described.

A somewhat different method of accomplishing the desired result consists in employin conductors of various diameters for the di erent sections of cable loaded in the same way with material of the same permeability. Since the inductance of the conductor under these conditions is inversely proportional to its diameter, the tapering of inductance may be obtained by varying the conductor diameter, employing a conductor of large diameter near the terminals and conductors of progressively smaller diameters in the middle portion of the cable. This method is also of advantage for the purpose of reducing signal distortion and interference between the received and transmitted signals due to variation of the magnetic characteristics of the loading material, since for a given value of current the value of the magnetic field inthe loading material is inverse- 1% proportional to the conductor diameter. he loading material is therefore worked at a lower magnetic flux density in the larger conductor and the variations in the resistance and inductance are less, or' of course both the diameter of the conductor and the amount of magnetic material per unit length of the cable may be simultaneously varied to produce similar results.

It is proposed, therefore, as an example of the present invention to employ conductors of some such type as here mentioned only in the parts of the cable where the-magnitude of the signal current is large; and for the greater part of the cable, where the amplitude of the signal current is such that the magnetic disturbances are negligible, to use a conductor loaded in the usual manner.

As an illustration of a method of design of a cable which is less susceptible to magnetic distortion than the ordinary type of cable, consider a case where signals are to be transmitted from both ends, not necessarily simultaneously and where the decreased slopepf resistance and inductance characteristics is obtained by sacrificing permeability. Referring to Fig. 4, the cable is shown at 10 ;with the conductor 11 (Figs. 5, 6 and 7) surrounded by a helical tape 12 of permalloy. The degree of loading is made least at the ends of the cable 10 and greatest at its middle portion. For convenience of manufacture, the cable is made in, sections, with uniform loadin foreach section. The ordinates of .the iagram at the i upper part of Fig. 4 show the degree of loading at corresponding points along the length of cable which are represented by the abscissae.

A procedure by whichthe lengths of the conductor sections and .the modlficationof inductance per section may be determined will now be outlined. In other words, this is a procedure for determining a satisfactory shape to give the diagram at the top of Fig. 4.

The cable is divided into sections accord ing to a tentative plan and the values of the fundamental signal currents in each section are determined andfrom them, the variations of L and F, and consequently the several induced voltages in the respective sections. 1

It is obvious that the current at a cable terminal, due to the voltages of any combination frequency or harmonic frequency mduced in one of the sections of the cable, can be represented vectorially in amplitude and phase. The resultant efiect at this frequency, due to the contributions from the entire cable, can then be obtained by combining these vectors by the well known graphical method which is shown in Fig. 8. For instance, i the cable is terminated in a non-loaded section, only negligible disturbing voltages will be induced in this section and the vector rep-' resenting the disturbing currents will be zero.

The sectionadjacent to the non-loaded section will contribute an amount represented by the vector ab of Fig. 8, the next adjacent section an amount be, the next 0d, and so on for allthe sections of the cable, and the resultant effect at the terminal, due to all the sections, will berepresented by thevector an, which is obtained by the method known as the polygon of vectors. Thisprocess is employed in turn for each of the harmonic and combination frequencies involved in the disturbance. w

For each frequency there is an upper limit to the value that the disturbing current can have before it interferes appreciably with the signal. A circle is drawn with the origin of vectors as center and the absolute value of. this upper limit as radius, and it is obvious that the condition of non-interference means that the extremity of the vector representing the resultant disturbing current must lie within the circle. If the extremity of the vector falls without the circle, aninspection of the vector diagram will show which of the several components is at fault and how this component can be reduced'in order to bring thevector within the prescribed limit. For instance, if the component ab in Fig. 8 representing the contribution of the first loaded section of cable, were several times the magnitude shown in the figure, the resultant vector, an, would probably fall outside the circle shown by the dotted line and the obvious remedyv in this case would be to decrease the amount of loading in this section or to increase the length of the non-loaded section of the cable.- On the other hand, the vector diagram may indicate that too great an allowance was made for distortion inthe tentative arrangement and'that heavier loading can be used in certain sections. The final design of cable is attained when each of the frequencies involved in the distortion satisfies the requirement above described.

The terminal sections of the cable may be constructed of non-loaded conductor so that practically no disturbance will originate in these arts of the cable. The sections may be of, suc length that the signal current at the end of the non-loaded section is reduced enough so that a section of conductor'with a small amount of continuous loading can then be used." This extends out to a point where a higher degree of loading possible, and so on until a point is reached where the most heavily loaded type of cable can be used..

- The procedure here stated can be applied for the design of cable for one-way or twobecomes i way operation but the final result may be different for the two cases. For a cable to be operated inonl one direction at a time 'the magnitude of t e received signal is comportion of the cable uniformly. Considerable improvement over uniform loading throughout the cable 'may thus be effected. The length of the non-loaded terminal sections may be only a few miles, or several hundred miles depending upon local disturbing conditions as well as the current attenuation.

The usual terminal apparatus is indicated diagrammatically in Fig. 4 with the receiver R across the Wheatstone bridge, the equal condensers O in two adjacent arms of the bridge, the transmitter T connected to the apex betweenthe condensers C and the bal-' I ancing network N This network and the line 10 form two arms of the complete Wheatstone bridge for the corresponding.

end of the cable. The network is made in sections N N etc., corresponding sign accordingly. In a balancing network, far more precision of adjustment is required for the part closest to the bridge, that is, the part N in the figure. It is much easier to construct this part and adjust it precisely the sections of. the line andof'different decurrent, and moreover, the effective resistance var es with current. Hence it Wlll be seen that the present modification by which a 2 graduation of loading is employed makes it easier to construct an artificial line to balance the cable than if the cable were loaded to the utmost degree all the way from one end to the other. e 1

In another aspect of the invention, which has been briefly mentioned above, the improvement from graduated loading arises from the fact that an optimum permeability may thus be obtained at all points along the conductor. When large sending currents are used, transmission can be improved by obtaining as nearly as possible the optimum value of loading throughout the length of the cable. The optimum value is that at which the increased gain (as measured for example in miles of standard cable in the well known manner) resulting from a small increase in permeability is just balanced by the resulting increase in eddy currents, hysteresis loss, and dielectric losses. The large currents at the sending end increase the effective permeability above its small-current value, and consequently, if it is desired to have optimum permeability under operating conditions, it will be necessary to employ on the terminal sections of the cable a loadingmaterial having a permeability which is less than that used on the remainder of the cable.

When, for other reasons herein discussed, it is of advantage to omit the loading from the terminal sections or to make it very light, this added advantage of obtaining or approaching the optimum value of permeability may be simultaneously realized. Thus, in general, the graded or tapered loading has several or all of the advantagesherein disclosed, to some degree at least.

An additional advantage of the cable having a tapered loading is that it is easier to balance for duplex operation than a cable that is loaded uniformly for high inductance for all its length. This is due to the fact that the heavier the loading of a cable, the more difficult and expensive is the construction of an artificial line to simulate the cable to within a certain percentage.

The reason why it is easier to construct an artificial line to balance a cable when the loading inductance is small can be seen from the following: Assuming the cable to be uniformly loaded and free from irregularities, the input impedance of the cable in the frequency range where most accurate balance is essential is equal to K, the characteristic impedance of the cable. If the artificial line is constructed of equal sections, each equivalent inceptito a length 8 of cable, then the electrical parameters of a section are 8R, sL, 8G and 80, where R, L, G and C are respectively the resistance, inductance, leakance and capacities of a unit length of cable. The input impedance of the artificial line at the frequency will then be, to a close approximation,

I 2 z= 1([1 (R+jp'L)(G+jp0)],

where 7' l and the unbalance due to the lack of equality between theinput impedances of the cable and of the artificial line is measured by the expression The curves of Fig. 10 give the value of P as a function of frequency for various degrees of loading. The values for the heavily loaded cable are ten to fifteen times those of the non-loaded cable and it is obvious that in order to reduce the unbalance for the loaded cable to the same level as the non-loaded cable unbalance, the sections of the artificial line corresponding to the loaded cable must be about one-quarter the size of the sections in the artificial line corresponding to the non-loaded cable. A given length of loaded cable will, therefore, require four times as many sections of artificial line to balance it as will the same length of non-loaded cable. This involves higher costs and greater comple'xity of structure of theartificial line.

An additional upper limit on the size of section of the artificial line is set as follows. The process of balancing a cable on which irregularities occur consists in placing on the artificial line irregularities corresponding in magnitude and location to those of the cable. To achieve a given degree of balance at any frequency, it is necessary that corresponding irregularities on the artificial line and on the cable shall differ in location by less than a certain fraction of a wave-length, and the length of section cannot be greater than this amount. In the two cases given above the wave-lengths at a frequency of 60 cycles per second are 100 miles for the loaded cable and 500 miles for the non-loaded cable. Therefore, the upper limit of size of section set by this criterion is again smaller for a loaded than for a nonloaded cable.

Four or five times as many sections will, therefore, be required to balance the cable at a given frequency when it is loaded. This means not only increased expense of construction but greater difiiculty of maintaining balance. From practical consideration a limit '11) can be set, corresponding to any degree of loading L which (Equation 5) cannot be decreased for reasons of economy or portion of cable and of the A, line. When a point on the ca le 1s reached Y structed and kept in balance. I

v 1 '1,": ea,o41.

I v u v i I i m efiiciency. The value of w mcreasesas the degree of loading L is increased.

It is known that the unbalance, du'e to'a local difference between the impedances of a corresponding portion of artificial line is less the greater the distance of these portions f minal. This is due to the fact that on both cable and artificial line the transmitted current is attenuated over the interval between the terminal and the impedance irregularity, and the current reflected from the irregularity is attenuated in a corresponding degree before it can reach the receiving instrument. Therefore, it is evident that the diflicult of constructing and maintaining an arti cial line to balance a uniformly loaded cable will be confined largely to a portion of the line within a certain distance fromthe terminal. The unbalance due to the remainder of the line will be diminished by the attenuation factor so that these sections can be made'of larger and more convenient size.

According to one aspect of the present instruction of the portion of the artificial line in the neighborhood of the terminal by employing a cable composed of a number of sections of various degrees of loading. It was previously pointed out that corresponding to each degree of loading L there is a limit 'w beyondwhich the imbalance between cable and artificial line cannot be decreased for reasons of economy or efliciency, and that the'ef fect of a. given unbalance decreases as it is moved away from the terminal. Starting at theterminal of the cable, as in the methods described above, a section with little or no load be balanced ing is employed, so that it canwith a comparatlvely simple ty of artificial where it is possible to tolerate greater unbal ance in the artificial line, a section of more heavily loaded cable is employed, the loading being such that the unbalance in the corresponding portion of the artificial line is less than the limit for this part of the system. This process is continued until a point is reached where the full degree of loading can be employed without causing severe requiretion. At the same time the values 'w ,'etc.,

. are large enough so that the corresponding portions of the artificial line are easily con rom the 'ter-' vention it is proposed to simplify the .con-' ments on the corresponding portion of'arti- To illustrate, we will consider the case where the cable contains sections of two degrees of loading, the major portion of the cable being heavily loaded and the terminal sections non-loaded. The characteristic impedances of the twotypes being Z; and Z respectively, it can be shown that the input impedance Z of the cable is'determined to a close approximation by the relation z Z (1+w 7 I w z =Z (1+'wand the input impedance 2 can be determined from a formula similar to (6) The unbalance currentin the receiving apparatus is determined by the quantity Z wr i- (w. 223 (7) where I I I I v w1 an i 2 4Z1 2 en (8) 1"1).Z z.+z. .The quantity 4);. measures the effect in the receiving apparatus of changing, at the point w, from non-loaded to loaded cable. It is evi dent that 10 (the unbalancebetween the loaded cable and the corresponding portion of artificial line) -can be much greater than w (the unbalance between the non-loaded cable and. its corresponding portion of artificial is, from the nature of the quantities concerned, less than or, at most, a little greater than 'unity, and the exponential is a fraction which decreases rapidly as w is increased. Taking for 'w and w the1r 'l1m1t1ng values,

itis possible to determine a-value of m for which v v Z is less than theprescribed value. Y The preceding discussion suggests a practical method of design of a cable of the proposed type. A tentativearrangcm'ent of sec-. tions is selected and the value of'(zZ)/Z is determined as the sum of a number'of terms Z the term 1),. being the effect ofthe unbalance betweenthe kth section of the cable and the corresponding portion of the artificialiline.

to a ca The various 'vs can be represented in amplitude and phase by vectors as shown in Fig. 9. The absolute value of the prescribed limit on unbalance interference is represented by the dotted circuit, and for efiicient operation it is necessary that 4; shall lie within this circle. In case n falls without the circle it is easy to tell which of the components '0 etc. is too large, and the design can be-changed accordmg lr The method of design that has just been outlined takes no consideration of the efiect of distortion and interference due to the loading material, which effect and its remedy were discussed in the first part of this specification. To correct for the effect of distortion and interference, as well as to meet the requirements of a balancing network, the design of the loading must be further modi-. fied to meet these additional requirements as outlined above. Incertain cases, however, it may be desirable to employ tapered loading for the sole purpose of decreasing sending voltage unbalance or to permit the use of less complicated balancing networks.

When a loaded cable is subjected to the pounding of waves or to the action of ocean currents, the motion of the cable will result in rapid variations of its inductance, which will have a disturbing effect on the signals. For this reason, also, it will be advantageous to reduce the degree of loading in thesesections or to remove it entirely.

The receding considerations apply also ble loaded by means of inductance coils. The degree of loading in this case can be regulated by varying either the inductance of the individual coils or the interval of cable between adjacent coils. v 1

What is claimed is:

1. A submarine cable which is inductively loaded for a considerable portion of its length and unloaded in a shallow water portion or portions.

2. A submarine cable continuously heavily loaded with magnetic material for a considerable portion of its length and unloaded in a shallow water portion or portions.

' 3, A submarine telegraph cable having great attentuation and loaded inductively, said loading being comparatively heavy in a part where the signaling current is relatively small due to its having been attenuated by the cable and comparatively light in a part in which the current is relatively large.

4. A signaling conductor loaded comparatively heavily in a part distant from the sending end and comparatively lightly in-a part near the sending end, and in combination therewith'a balancing network with parts designed to correspond respectively with the differently loaded parts of the conductor.

5. A signaling conductor, part at leastof which is loaded continuously with material the permeability of which is a variable dehaving variable permeability dependent upon the current in the conductor so that the inductance and elfective resistance of the conductor vary substantially with the current in the conductor, the degree of loading being greatest where the signaling current is relatively small due to its having been attenuated by passage through the conductor and progressively less in parts where the current is relatively large.

7. A signaling conductor having large attentuation and having non-loaded terminal sections and other sections having progressively heavier loading toward the mid-point of theconductors 8. A submarine cable having great attenuation comprising a signaling conductor having non-loaded terminal sections at least several miles in length and magnetic material associated with the remaining portion of said conductor to form continuous inductive loading. 1

9. A submarine cable having great attenuation comprising a signaling conductor,

part at least of which has a graduated continuous, loading of a nickel-iron alloy having higher permeability than iron at low magnetizing forces, the degree of loading being greatest where the signaling current is relatively small due to its having been attenuated by the cable and progressively less in parts where the current is relatively large.

10. A signaling conductor having great attentuation and having I a part, at least, loaded with material whose hysteresis loss is a variable dependin upon the current in the conductor, the loading being heavy where the signaling current is small due to its having been attenuated by passage through the conductor nd comparatively light where the current is relatively large.

11. An inductively loaded signaling conductor surrounded by solid insulating material, the loading being comparatively heavy in a part in which signal distortion due to variation with current of an electric charac teristic of the loaded and insulated conductor is small, and comparatively light in a part in which the signal current is so large that its distortion would be appreciable if heavy loading were applied.

12. The combination with a signaling conductor loaded comparatively lightly in a portion at its sending end andheavily in a portion distant from the sending end, of means for impressing upon said cable at the sending end a signaling voltage of such value that the resulting current in the lightly loaded sectlon would be unduly distorted by the action of the loading material if heavy loading were there applied, but wouldbe so greatly attenuated before reaching the heavily loaded section that no serious distortion would there occur.

13. A submarine cable heavily loaded throughout a part of its length with a nickeliron alloy, sa1d alloy having higher permeability than iron at magnetizing forces of a few tenths of a gauss qrlessand being highly sensitive to mechanical strain, a port-ion of the cable in shallow water being unloaded.

14. A- submarine cable having a nonloaded terminal section and angtherjsection which'is'heavily loaded'with magnetic material, and in combination therewith abalancing network with parts designed to correspond, respectively, with the non-loaded and loaded parts of the cable.

15.'A submarine cable having large attenuation and having non-loaded terminal sections and other sections having progres sively heavier'loading toward the mid-point of the cable, and in combination therewith a balancing network with parts desi ned to oorres 0nd, respectively, with the di erently loade arts of the cable. 30. 16. e :method of signaling by electric currents over a conductor with hi h attenuation without serious distortion w ich consists in subjecting the signaling currents to the reaction of a magnetic flux induced by them in a continuously a plied loading material after, and only a ter, they have be- .come attenuated greatl by passage through an unloaded portion 0 the conductor.

.17. The method of signaling by electric currents over a conductor without serious dis-i tortion, which consists in'producinga magnetic flux in association approximately with the reduction of the currents by attenuation.

18. The method of signaling by electric.

currents over a conductor without serious disj tortion which consists in subjecting the signaling currents to the reaction of a magnetic flux induced relatively great in certain parts'of the conductor where the current is relatively small due to its having been attenuated by passage.

through the conductor and relativelyv low 1n certain other parts where the current is I larger. v v v v 19. The method of, signaling by electric currents over a submarine cable conductor without serious distortion which consists in subjecting the signaling currents throughout at leastthe major portion of'the conductor to the reactionof a magnetic flux induced by them, and limiting .the flux I everywhere so tlatfithe hysteresis loss has no' appreciable 6516 cc v 1 V sending end, which comprises employinga connecting said portions of said artificial line in series whereby one of the portions of said cable system and an artificial line conwith the conductor and making its relative intensity correspond bl S t by them, making this reaction.

20. The method of operating a signaling conductor which is inductively loaded com-.

' paratively lightly in a portion at its sending end and heavlly in a portion distant from the signaling current so large that undue distortion would be producedin the'li htly loaded portion if it were-heavily loade but not so large as to cause undue distortion in the heavily loaded portion. u

21. The method of balancing the constants of an extended cable, having loaded and nonloaded portions, which comprises separatline into a plurality of portions and adjusting one of said ortions to balance the non-loaded portion 0 said cable and adjusting another portion of said artificial line for balancing the loaded portion of said cable. 1 I

' 22. The method ofbalancing the constants of an extended cable;\having loaded and nonloaded ortions, which comprises separating an arti cial line into a plurality of portions,

ing an artificial said artificial line balances the loaded portion of said cable and another portion of said artificial line, balances the non-loaded portion of said cable.

23. A cable system comprising in combination. an extended electrlc cable having a loaded portion and a non-loaded ortion oneach end thereof, duplex transmitting and receiving apparatus connected at each. end of nected at each end of said cable system, each of said artificial lines comprising a pa1r 0 portions having difiering electrical char-' acteristics, one of saidportions o erating to balance the non-loaded-portion 0 said cable system and the other 0 said portions operating to balance the loaded portion of said ing a portion for balancing the non-loaded ortion of said cable and a separate portion or balancing the loaded portion of said cable, the portions of said artificial lines being electrically connected in series with said portion of sa1d artificial line for balancing the non-loaded portion of said cable connected adjacent the end of said cable.

25.. An electric signaling system, comprising in combination a cable, including a loaded portion and a non-loaded portion at each end thereof, duplex signaling apparatus connected to opposite ends of said cable and an artificial line' at opposite ends of said cable lau and connected with said signaling apparatus,

said artificial line consisting of a pair of portions, each having electrical characteristics, differing one from the other, the electrical characteristics of one portion of said artificial line simulating the electrical characteristics of the loaded portion of said cable and the other portion of said artificial line having electrical characteristics simulating the electrical characteristics of the non-loaded portion of said cable.

26. An electric signaling system, comprising in combination a cable, said cable having a loaded portion and a non-loaded portion, signaling apparatus connected to each end ofsaid cable and an artificial line connected with each end of said cable, said artificial line having a plurality of portions, one of said portions being arranged to balance the electrical constants of said non-loaded por-- tion of said cable and the other portion of said artificial line being arranged to balance the loaded portion of said cable, said first mentioned portion of said artificial line being connected intermediate the end of said cable and said second mentioned portion of said artificial line.

27. An artificial line, for balancing a cable, having a loaded portion and a non-loaded portion, said artificial line including a pair of'separate portions for electrically balancing the loaded portion and the non loaded portion of said cable, one portion of said artificial line including resistance and capacity, and the other portion of said artificial line including inductance, resistance, and capacity.

28. An artificial line for balancing a cable, having a loaded portion and a non-loaded portion, said artificial line including a pair of separate portions for electrically balancing the loaded portion and the non-loaded portion of said cable, one portion of said artificial line including a resistance and capacity. and the other portion of said artificial line including inductance, resistance and capacity, said last named portion of said artificial line being connected in series with said first mentioned portion of said artificial line with said first mentioned portion of said artificial line interposed between the end of said cable and said second mentioned portion of said artificial line.

29. A submarine cable in' which a section near a terminal thereof and. a section near the center thereof are loaded with magnetic material, the loading being such that the flux density in the loading material produced by a given small current traversing the first named section is smaller than that produced in the loading material by an equal current traversing the second named section.

30. A loaded submarine cable having the loading material graduated in such a way that a smaller flux density is produced in the magnetic loading material near a cable end than is produced in the loading material of a sect-ion near the center of the cableby the 33. A continuously loaded submarine cable conductor having central portions loaded with material of greater permeability at a given density of signaling current than the permeability of loading of a terminal section at the same density of signaling current.

34. A submarine cable comprising sections of cable the impedances of which vary with variations in current but in difierent degree for different sections, characterized in thls, that the sections undergoing the least variation in impedance over a given range of current intensity are located at points 1n the cable where ,the variation in intensity of mgnaling currents is greatest.

35. A submarine cable in which a section near a terminal thereof and a section near the center thereof are loaded with magnetic material, the loading being such that the variation in the flux density in the loading material produced by a given variation in the current traversing the first section is less than that produced in the loading material by an identical variation in the. current traversing the second named section.

36. A submarine cable in which a section near a terminal thereof and a section near the center thereof are loaded with magnetic material, the loading being such that for given variations in current intensity in the two sections the variation in the resistance introduced by the loading material of the first section is less than that of the second section.

37. An electric conductor comprising a plurality of continuously loaded sections, the self-inductance of each section gradually increasing from the ends of the conductor toward one of the sections.

38. An electrie conductor comprising a plurality of continuously loaded sections, the self-inductance of each section gradually increasing from one end of the conductor toward the other.

In witness whereof, I hereunto subscribe my name this 28th day of February, A. D.

- JOHN J. GILBERT. 

